The police in nimbin just don't care.... we drive in, we park, we get out of car, people run over and ask us if we want to buy weed, the scoot down the alley thingo and sort it out and while we wait some lady comes over and asks if we'd like to buy some cookies too, we finalise our purchase, hop in the car and carry on our way - all within a block or 2 of the police station *shrug*
We have passed several police cars coming out of Nimbin and we've never been stopped. We've sat on a busy beach in Byron and smoked weed and never been questioned by anyone.
It's not to say you definitely wont be stopped, questioned or charged... but the likelihood of it is low, imo... as others have said, just try not to advertise it and if possible, travel in an "average" looking car, as opposed to one that would draw attention (i.e. hotted up car/total bogan mobile).